Parsing the application of PHP dirname () and __file__ constants _php techniques

__FILE__ indicates that the absolute path of the current file includes the filename, dirname (__file__) represents the absolute path to the current file, and basename (__file__) represents the file name of the current file, DirName (__file__). " /f/". BaseName (__file__) represents the file under the F directory in the directory of the current file, which is called dirname (__file__), and require indicates that the file is included in the file.
Here is a detailed explanation:
1 The dirname (__file___) function returns the path where the script is located.
For example, file b.php contains the following:
<?php
$basedir = DirName (__file__);
?>
If b.php is referenced by a.php file require or include in other directories.
The contents of the variable $basedir or the path of the folder where b.php resides.
Instead of becoming the directory where the a.php file resides.

2) dirname (__file__) typically returns the directory structure of the current directory of the file to the system root directory.
The current file name is not returned.
DirName (__file__) may also return one. (current directory)
The reason is that the b.php file is in the default Web directory of the http.conf or PHP configuration development environment.
For example, Web_root is: "c:/root/www/".
The b.php file path is: "c:/root/www/b.php".

3) Using the method hint,
If you repeat, you can elevate the directory up one level:
For example: $d = DirName (dirname (__file__));
The fact is that a directory for dirname () to do the parameters. Because DirName () returns the last directory without \ or/
So when you reuse it you can assume that dirname () treats the lowest directory as a filename. Return as usual
The parent directory of the current directory. So the repetition gets the directory of its upper level.

4 contains files that are available at the previous level of the directory
Include (DirName (__file__). " /.. /filename